Siemens SIPROTEC 7UT613 series Manual page 224

2 Functions
Hot-Spot Calcula-
tion
224
If extra liquid coolants are available, the following types of coolants can be used:
• ON (Oil Nnatural = (naturally circulating oil): Because of emerging differences in
temperature the coolant (oil) moves within the tank. The cooling effect is not very
intense due to its natural convection. This cooling variant, however, is almost noise-
less.
• OF (Oil Natural = forced oil circulation): An oil pump makes the coolant (oil) move
within the tank. The cooling effect of this method is therefore more intense than with
the ON method.
• OD (Oil Directed = forced-directed oil circulation): The coolant (oil) is directed
through the tank. Therefore the oil flow is intensified for sections which are extreme-
ly temperature-intensive. Therefore, the cooling effect is very good. This method
has the lowest temperature rise.
The hot-spot temperature of the protected object is an important status value. The
hottest spot relevant for the life-time of the transformer is usually situated at the insu-
lation of the upper inner turn. Generally the temperature of the coolant increases from
the bottom upwards. The cooling method, however, affects the rate of the temperature
drop.
The hot-spot temperature consists of two parts:
• the temperature at the hottest spot of the coolant (included via RTD-box),
• the temperature rise of the winding turn caused by the transformer load.
RTD box 7XV5662-xAD can be used to acquire the temperature of the hottest spot. It
captures the temperature value and transmits these to the respective interface of de-
vice7UT613/63x. The RTD box 7XV5662-xAD is able to acquire the temperature at up
to 6 points of the transformer tank. Up to two RTD boxes of this type can be connected
to a 7UT613/63x.
The device calculates the hot-sport temperature from these data and the settings of
the main properties. When a settable threshold (temperature alarm) is exceeded, an
annunciation and/or a trip is generated.
Hot-spot calculation is done with different equations depending on the cooling method.
For ON–cooling and OF–cooling:
For OD-cooling:
Θ
Temperature of the hot spot
h
Θ
top oil temperature
o
H hot-spot factor
gr
k load factorI/I (measured)
N
Y winding exponent
In this aspect, the load factor I/I
the overload protection is assigned. The phase information is taken from the con-
cerned phase in case of generators, motors, etc., or y- or z-connected transformer
windings; in case of delta-connected transformer windings the difference current is
taken. The rated current is that of the corresponding side.
is determined from the currents of that side to which
N
7UT613/63x Manual
C53000-G1176-C160-2